1. Field of the Invention
The present invention generally relates to fiber optic termini, and more particularly to pin and socket fiber optic termini. By pin and socket termini is meant termini of the type in which a pair of optical fibers are connected by installing each fiber in a hole in a precision ferrule, and positioning the ferrules in alignment with their tips abutting. A first or socket ferrule lies in the rear half of an alignment sleeve of a socket connector, and a pin connector is mated to the socket connector by projecting the pin ferrule into the sleeve until the tips of the ferrules abut, the socket ferrule being spring biased forwardly so it can deflect rearwardly.
In addition to relating to improved pin and socket termini, the present invention relates to a method of terminating fiber optic cables to fiber optic termini.
2. Description of the Related Art
Pin and socket fiber optic termini of the type in which a pair of optical fibers are connected by installing each fiber in a hole in a precision ferrule, and positioning the ferrules in alignment with their tips abutting, are well known and widely used. However, conventional pin and socket fiber optic termini have a number of limitations which makes them impractical for use in couplers requiring a terminus size of less than size 16. The present invention is directed to the following improvements to the conventional pin and socket fiber optic termini, which are intended to simplify manufacture and thereby enable production of smaller termini: (i) re-design of the holders or retention sleeves, precision ceramic guides, and biasing arrangements for the termini to permit the holders and guides to be press-fit together, avoiding the need to use adhesives or laser welds during assembling of the terminus structures (although adhesives may still be used during termination of the fiber optic cables to the pin and socket termini); (ii) re-design of the portion of the termini to which the strength members of the cable are terminated, simplifying the termination procedure and providing a more secure termination; (iii) including features that facilitate replacement of parts, cleaning and polishing of the mating faces of the precision guides or ferrules after a cable has been terminated thereto, and formation of a good environmental seal at the ingress of the terminated cable into a pin and socket coupler.
FIGS. 1A and 1B illustrate a conventional pin and socket fiber optic connector system. The conventional termination arrangement includes a pin connector 1 and a socket connector 2 arranged to accommodate a plurality of pin termini 3,3xe2x80x2 and socket termini 4,4xe2x80x2. Pin termini 3,3xe2x80x2 and socket termini 4,4xe2x80x2 are arranged so that the pin and socket connectors can conveniently be mated by simply inserting ends of the pin termini 3,3xe2x80x2 into openings in the socket termini 4,4xe2x80x2 and then securing the pin connector 1 to the socket connector 2 using any of a variety of known coupling means (not shown). Examples of known types of coupling means that can be used in connection with pin and socket fiber optic termination arrangements of the illustrated type include threaded coupling nuts and bayonet-type coupling arrangements.
One of the pin termini 3 of the connector system of FIG. 1A is shown prior to mating and another of the pin termini 3xe2x80x2 is shown in a mated position. Each pin terminus includes a ceramic guide 5 for precisely locating an optical fiber, and a guide holder 6, conventionally made of stainless steel, for holding the ceramic guide. The retention sleeve 6 is conventionally secured to the precision guide by adhesives or welding, and includes an integral rear ferrule to which the strength member and/or jacket of the cable is terminated after being stripped back from the fiber, and after insertion of the fiber through the retention sleeve 6 into the precision guide 5. The completed pin termini are mechanically held in the pin connector 1 by retention tines 8 that engage a collar 9 on the retention sleeve, and the coupler is completed by the inclusion of a sealing gasket 11 at the mating interface of the pin coupler, and a sealing grommet 12 that engages the rear of the retention sleeve 6 and cable jacket 7 extending therefrom to prevent ingress of moisture or dust into the coupler.
The socket termini 4,4xe2x80x2, shown in greater detail in FIG. 1B, also include precision ceramic guides 13 and guide retention sleeves 15 to which strength members and/or jackets 16 of the fiber optic cables are terminated, and in addition includes an arrangement for biasing the retention sleeve 15 and guide 13 of respective socket termini 4,4xe2x80x2 against the retention sleeve 6 and guide 5 of corresponding pin termini 3,3xe2x80x2. Furthermore, the socket termini 4,4xe2x80x2 each includes a biasing arrangement in the form of a compression spring 17 that engages a rear of the corresponding retention sleeve 15 and is captured between the retention sleeve 15 and a rear ferrule or cap 18 to which the cable is terminated. Rear ferrule 18 is secured, through use of an adhesive or welding, to an alignment sleeve 19 which axially aligns the ceramic guides of the pin and socket connectors, and which surrounds the retention sleeve 15 to guide the retention sleeve while permitting axial movement of the retention sleeve during mating.
An opening 20 in the alignment sleeve serves as the socket opening for receiving corresponding precision guide 5 of one of the pin termini 3,3xe2x80x2. The socket termini 2 are secured in the socket connector, in the illustrated connector system, by engagement between a collar 21 on the alignment sleeve 19, and retention tines 22 similar to the corresponding retention tines of the pin connector, although it is also possible to arrange the rear ferrule 18 to engage the retention tines. At the rear of retention sleeve 15 is a space 23xe2x80x2 that permits movement of guide 13 and retention sleeve 15 in a rearward direction against the bias provided by spring 17 in response to insertion of guide 5 into alignment sleeve 19. Conventionally, the strength member of the cable is secured to a rear portion of rear ferrule member 18 by crimp ferrule 25, and a sealing rear grommet 23 corresponding to sealing grommet 12 is provided at the rear of the socket connector 2 to complete the connector system.
As mentioned above, the design illustrated in FIG. 1, as well as other similar pin and socket fiber optic termination designs, are impractical for terminus sizes of less than 16. One reason is that the precision ceramic guide and guide retention sleeve of the conventional pin and socket termini (or the alignment sleeve and rear ferrule or cap of the conventional socket terminus), must be secured to each other through use of adhesives or precision welding techniques. The design of the socket terminus, in particular, necessitates the use of adhesives or welding because of the manner in which the bias spring is captured within the alignment sleeve. This use of adhesives or welding becomes increasingly difficult to carry out as the terminus size is decreased, resulting in increased assembly costs and likelihood of errors. Furthermore, once the rear ferrule is adhered or welded to the alignment sleeve, non-destructive removal of the precision guide from the assembly is impossible. As a result, should an error occur during assembly or cable termination, or should one of the parts of the terminus prove defective, the entire terminus must be discarded, further increasing costs.
A second problem that arises in smaller fiber optic terminations is that a smaller termination area for the cable strength member makes termination of the cable to the terminus difficult. Conventional designs do not leave sufficient room to provide a secure mechanical termination of the strength member to the rear of the guide retention sleeve in the pin termination, or to the rear of the rear ferrule in the socket termination, and the strength member itself may be too weak in a smaller cable to ensure that the cable is secured to the terminus while relieving stress on the optical fiber.
Additional problems with smaller size terminations include (i) difficulties in achieving an effective seal between the cable jacket and the rear sealing grommet, as a result of tolerances in the cable jacket, (ii) difficulties in maintaining a clean interface once the optical fiber is terminated to the precision guide, and (iii) in the case of single mode fiber terminations, difficulties in producing holes of sufficient length in the precision ceramic guides that hold the fibers.
It is accordingly a first objective of the invention to provide a pin and socket fiber optic termination system, in which the size of the termini may be made smaller than is practical for conventional fiber optic termini.
It is a second objective of the invention to provide fiber optic termini of the type including ceramic guides, retention sleeves, and a compression spring for biasing the retention sleeve and guide into a mating position, in which the ceramic guide, retention sleeve, and compression spring may be press-fit to each other without requiring laser welding or adhesives to secure the parts together during fabrication of the termini prior to termination of a cable.
It is a third objective of the invention to simplify termination of fiber optic cables to pin and socket termini and yet to improve the integrity of the resulting termination.
It is a fourth objective of the invention to provide a fiber guide assembly that can easily be removed and as necessary replaced up to the time a fiber optic cable has been terminated thereto.
It is a fifth objective of the invention to provide a fiber optic terminus which requires less frequent cleaning, and which has a relatively smaller diameter end face, enabling faster polishing times for a bonded in fiber.
It is a sixth objective of the invention to provide a fiber optic terminus designed to ensure that the rear grommet of an environmentally sealed connector will always seal on a consistent diameter and not be cable dependent.
It is a seventh objective of the invention to provide a guide assembly for a single mode fiber that provides an extended terminus while minimizing the length of the hole that must be produced in the ceramic guide.
It is an eighth objective of the invention to provide a multimode or single mode fiber optic cable termination arrangement that is simple in structure, reliable, and yet smaller than conventional fiber optic termini, capable for example of fitting into a size 20 pin and socket cavity within a connector.
These objectives of the invention are achieved, in accordance with the principles of a first preferred embodiment of the invention, by providing a fiber optic connector system and a termination arrangement for fiber optic cables in which the retention sleeve for the precision ceramic guides of the pin and socket terminations is arranged to receive and be secured to the precision ceramic guides solely by press-fitting, without the need for adhesives or welding. Both the pin terminus and socket terminus of this preferred embodiment include extended ceramic guides and guide retention sleeves, the socket terminus including a bushing and a stepped washer to capture the bias spring and retain it directly on the precision ceramic guide. Each of the retention sleeves of the pin and socket termini include precision angled steps arranged to facilitate press fitting of the guide retention sleeves to their respective guides and to make insertion of the terminus insertion/removal tool easier when using the smallest size fiber optic cable.
The structure of the termini of this embodiment has at least the following advantages: (i) positioning of the bias spring on the precision ceramic guide minimizes the radius of the socket terminus, (ii) addition of the stepped washer eliminates the need for capturing the bias spring by using adhesives to secure a conventional rear ferrule or cap to the retention sleeve or alignment sleeve, and allows the retention sleeve to move with the cable so that the cable can be directly terminated to the retention sleeve, (iii) the inclusion in the washer of a step prevents the retention mechanism of the connector from being deflected beyond the elastic limit of its material, and (iv) the sleeve is designed so that the grommet of the connector will always seal on the consistent diameter of the sleeve and not be cable dependent.
Due to the close tolerances, the frictional forces between the alignment sleeve and the guides causes the sleeve to stay on the socket terminus when the termini are disconnected and yet it is still easy to remove the sleeve for cleaning the front face of the guide. In addition, each guide member also has a long chamfer at one end which minimizes the size of the front face for faster polishing and which minimizes contamination of the front face by particles which may be sheared off of the alignment sleeve during assembly, and the length of each terminus may be chosen so that any grommet on an environmentally sealed connector will always fall on a portion of the body which has the same diameter for each terminus so that one grommet can be used with a variety of different size cables.
In accordance with the principles of a second preferred embodiment of the invention which is especially suitable for use with single mode optical fibers, which require a smaller core diameter for the precision hole than multimode optical fibers and therefore present additional tolerance/size problems, the guide retention sleeve is extended through the stepped washer and terminates in a threaded portion onto which the bushing may be threaded, the precision ceramic guide being press fit into the bushing rather than the sleeve so as to minimize the length of the hole that must be produced in the precision ceramic.
Like the termination arrangement of the first preferred embodiment of the invention, the retention sleeves of the termination arrangement of the second preferred embodiment of the invention provide the following advantages: (i) positioning of the bias spring on the retention sleeve (behind the ceramic guide) minimizes the radius of the socket terminus, (ii) addition of the stepped washer eliminates the need for capturing the bias spring by using adhesives to secure a conventional rear ferrule or cap to the retention sleeve or alignment sleeve, and allows the retention sleeve to move with the cable so that the cable can be directly terminated to the retention sleeve, (iii) the inclusion in the washer of a step prevents the retention mechanism of the connector from being deflected beyond the elastic limit of its material, and (iv) the sleeve is designed so that the grommet of the connector will always seal on the consistent diameter of the sleeve and not be cable dependent.
In addition to providing improved termini structure suitable for use with single mode and multimode optical fibers, the preferred embodiments of the invention share an improved arrangement for terminating the strength members of the cables to the termini, the method of termination also constituting part of the claimed invention. This method involves stripping the cable jacket from the strength member, fitting the strength member over a reduced diameter portion of the retention sleeves for the precision ceramic guides, coating the reduced diameter portion of the retention sleeves and a portion of the cable jacket with epoxy, surrounding the epoxy coating with a heat shrink sleeve, and applying heat to the assembly in order to cure the epoxy and complete the termination. By applying epoxy to the stepped down diameter of the rear bodies and the fiber optic cable jacketing, the strength member can be evenly distributed over the rear of the bodies and the shrink tube can be brought up over the outer jacketing of the fiber optic cable to the appropriate position and shrunk down in order to cure the epoxy, captivate the strength member, and seal the shrink tube to the fiber optic cable jacketing.
In an especially preferred embodiment of the invention, the heat shrink tube is made of an at least partially transparent material so as to provide a visual indication as to when the epoxy has changed color, thereby indicating whether the epoxy is fully cured.
As a result of the various improvements to the conventional pin and socket fiber optic connector provided by the above-described preferred embodiment of the invention, the size of fiber optic pin and socket termini can in practice easily be reduced from size 16 to size 20 and smaller. Nevertheless, even though the invention facilitates manufacture and use of smaller fiber optic termini, the scope of the invention should not be limited to size 20 and smaller termini. Instead, it is intended to encompass any size of fiber optic termini, for which the invention may offer improved reliability and ease-of-manufacture apart from the advantages of miniaturization.